The effect of dipeptidyl peptidase-IV inhibition on bone in a mouse model of type 2 diabetes.

Division of Endocrinology, Diabetes and Bone Diseases, Department of Medicine, Mount Sinai School of Medicine, New York, NY, USA.

Abstract

BACKGROUND:

Individuals with type 2 diabetes (T2D) are at greater risk of bone fractures than those without diabetes. Certain oral diabetic medications may further increase the risk of fracture. Dipeptidyl peptidase-IV (DPP-IV) inhibitors are incretin-based therapies that are being increasingly used for the management of T2D. It has been hypothesized that these agents may reduce fracture risk in those with T2D. In this study, we used a mouse model of T2D to examine the effects of the DPP-IV inhibitor, MK-0626, on bone.

METHODS:

Male wild type (WT) and diabetic muscle-lysine-arginine (MKR) mice were treated with MK-0626, pioglitazone, alendronate or vehicle. The effects of treatment with MK-0626 on bone microarchitecture and turnover were compared with treatment with pioglitazone, alendronate and vehicle. Osteoblast differentiation was determined by alkaline phosphatase staining of bone marrow cells from WT and MKR mice after treatment with pioglitazone, MK-0626 or phosphate buffered saline.

RESULTS:

We found that MK-0626 had neutral effects on cortical and trabecular bone in diabetic mice. Pioglitazone had detrimental effects on the trabecular bone of WT but not of diabetic mice. Alendronate caused improvements in cortical and trabecular bone architecture in diabetic and WT mice. MK-0626 did not alter osteoblast differentiation, but pioglitazone impaired osteoblast differentiation in vitro.

CONCLUSIONS:

Overall, the DPP-IV inhibitor, MK-0626, had no adverse effects on bone in an animal model of T2D or directly on osteoblasts in culture. These findings are reassuring as DPP-IV inhibitors are being widely used to treat patients with T2D who are already at an increased risk of fractures.

Weekly body weights of the MKR mice treated with vehicle, pioglitazone (Pio), MK-0626 or alendronate (Alend) revealed that there was no significant difference in percent of body weight gained in any treatment group compared with the vehicle-treated mice (1A). NMR body composition analysis revealed no difference in percent fat mass (1B) or percent lean mass (1C) in any of the MKR treatment groups after 8 weeks of treatment (n = 9–21 per group). Graphs represent means for each group, and error bars indicate standard error of the mean

Random blood glucose levels in the MKR mice at baseline (8 weeks) and biweekly during the treatment period (Figure 2A). The MKR pioglitazone-treated group had higher glucose levels than the vehicle-treated group at baseline (* is the p value <0.05), but no differences were detected between groups for the remainder of the treatment period (n = 9–21 per group). A glucose tolerance test was performed with 2 g/kg glucose in the MKR vehicle and MK-0626-treated group. No statistically significant difference in glucose tolerance was detected between the MKR vehicle and MK-0626 groups (n = 4–11 per group). Plasma dipeptidyl peptidase-IV (DPP-IV) concentrations were found to be significantly elevated in the WT and MKR mice treated with MK-0626 compared with vehicle-treated mice (Figure 2C). (* is the p value <0.05, n = 6 per group). Graphs represent means for each group, and error bars indicate standard error of the mean

Representative images of alkaline phosphatase staining of WT (3A)-derived and MKR (3B)-derived bone marrow stromal cells after treatment for 14, 21 or 28 days with PBS, pioglitazone or the dipeptidyl peptidase-IV inhibitor MK-0626. The alkaline phosphatase staining experiments were performed in triplicate. Figure 3C–E show the quantification of the number of alkaline phosphatase positive colonies (>20 cells per colony). Graphs represent means for each group, and error bars indicate standard error of the mean. * is the statistically significant difference between pioglitazone treatment and phosphate buffered saline (PBS) treatment of wild type (WT) cells, and # is the statistically significant difference between MKR pioglitazone and PBS treatment of WT cells. Ŧ is the statistically significant difference between MK-0626-treated WT-derived and MKR-derived cells

MK-0626 treatment led to no changes in the gene expression in bone marrow cells derived from wild type (WT) or MKR mice. Gene expression analysis was performed by extracting total RNA from WT-derived or MKR-derived bone marrow stromal cells after 28 days of treatment with phosphate buffered saline (PBS), pioglitazone (PIO) or MK-0626 as described in the materials and methods. Experimental conditions were performed in triplicate, and gene expression for each sample was analysed in triplicate. MK-0626 led to no significant changes in gene expression compared with PBS treatment. Pioglitazone treatment led to an increase in PPARγ (4A) and a non-significant increase in the expression of adipocyte differentiation genes in cells derived from WT mice (4B). A decrease in osteocalcin (4C), with non-significant decrease in osterix expression (4D) was observed in cells from MKR mice treated with pioglitazone. Significant increases in expression of beta catenin (4E) and non-significant increases in Runx2 (4 F) and RANKL (4G) were observed in the pioglitazone-treated cells derived from the WT mice. Graphs represent means for each group, corrected to the WT saline treated group, and error bars indicate standard error of the mean.* is the p value <0.05 versus WT PBS-treated cells